A well-known anti jamming technique useful in attenuating the influence of a jamming signal when determining geolocation is known as space frequency adaptive processing (SFAP). Space frequency adaptive processing works to eliminate a jamming signal in both a spatial domain and a frequency domain. Such techniques rely on Fourier transformations in order to determine frequency domain information.
Space frequency adaptive processing works well when there is a stable jamming signal. However, if the frequency of a jamming signal changes or if its amplitude pulses over the course of a block of anti jam processing, the space frequency adaptive processing algorithms will not be as effective as they otherwise could be.
When the frequency of a jamming signal changes, for example when the jamming signal sweeps across a given frequency band, the bandwidth of the jamming signal appears to be greater than it really is. For example, if, over the course of a block of processing, the frequency of the jamming signal changes from 0 Hz to a Nyquist rate, the jamming signal would appear to be a broadband, low power signal. This would force the use of a broadband spatial null in the anti jam processing instead of a localized elimination of the jamming signal at a particular frequency at that same spatial location. This reduces the ability of the anti jamming system to attenuate the effects of a jamming signal and results in increased signal distortion.
Similarly, when a jamming signal is pulsed on and off, an anti jamming system may be forced to assume that a jamming signal is present during an entire block of anti-jam processing. This, too, results in sub-optimal anti jamming performance. This is because the weighting factors that are used to counter the jamming signal that are applied to various spatial perspectives of a signal at different frequencies will be constant. This results in attenuation at a consistent level even though the jamming signal is not present at all such spatial-frequency combinations.